I always run out of memory (start feeling laggy) with Firefox (10+ tabs) & Chrome (5+ tabs)
Chrome has its Task Manager, but Firefox is famous for its memory leak...
Until I find this: Memory Fox
Attempting to reduce the browser's RAM Memory usage promoting the increase of available RAM memories for other application processes RAM memory requirements. Hopefully, fostering any attempts of Memory Recovery and Retention.Just install it! It supports Firefox 6 and 7 too!